We use the OneNoteImporter.dll introduced by http://blogs.msdn.com/b/andrew_may/archive/2005/02/14/372450.aspx and there seems to be no update available for newer versions of OneNote Office other than 2003 SP1 for now.
It is designed as a IBlogExtension, a plugin - as such it can be changed independently of the main branch. So if you like to provide a patch for newer releases (or someone else), you are welcome.